Hydraulically-actuated operating mechanism for an electric circuit breaker



May 19, 1964 P. BARKAN 3,133,47

HYDRAULICALLY-ACTUATED OPERATING MECHANISM FOR AN ELECTRIC CIRCUIT BREAKER Filed Nov. 22, 1960 4 Sheets-Sheet 1 kn IEF VA VI Inventor: Philip Barkan,

b B Attorneg.

May 19, 1964 P. BARKAN 3,133, 7

HYDRAULICALLY-ACTUATED OPERATING MECHANISM FOR AN ELECTRIC CIRCUIT BREAKER Filed Nov. 22, 1960 4 Sheets-Sheet 2 Inventor: Philip Barkan,

Attorney.

May 19, 1964 P. BARKAN 3,133,475

YDRAULICALLY-ACTUATED OPERATING MECHANISM FOR AN ELECTRIC CIRCUIT BREAKER Filed Nov. 22, 1960 4 Sheets-Sheet 3 V a 3 q g WITH CHECK VAL v5 {f WITHOUT k CHECK VAL VA 5 OPEN I FULLY ope-Iv I l y l WITH CHECK m1 v5 j g F A\ II"\ a I x- 1 W J flCCL/MULAT'OI? PREsSl/R: 3 WITHOUT CHECK wu v5 t q 3 l I I l I I 1 a a 8.3 4/ a: m TRIP CONTROL T/ME' //v 6764 56 SIG/VAL VALVE amass I n v e n t o T? Philip Bark a'r May 19, 1964 P. BARKANY 3, 7

HYDRAULICALLY-ACTUATED OPERATING MECHANISM FOR AN ELECTRIC CIRCUIT BREAKER Filed Nov. 22, 1960 4 Sheets-Sheet 4 Fig.4.

RELIEF VALVE Inventor: Ph Hip Barkan,

by Attorney.

United States Patent HYDRAULICALLY ACTUATED ()PERATENG lvlECHANlEiM FQR AN ELECTllllC CIRCUIT BREAKER Philip Barlran, Lima, Pm, assignor to General Electric Company, a corporation of New York Filed Nov. 22, 196%, Ser. No. 7&9??? 8 Claims. (Cl. 91-44d) This invention relates to an operating mechanism for an electric circuit breaker and, more particularly, to a hydraulically-actuated operating mechanism for a circuit breaker of the automatic reclosing type.

The usual hydraulically-operated circuit breaker comprises a fluid motor that is operable to close the breaker, an accumulator for supplying pressurized operating liquid to the motor, and a normally-closed control valve for controlling the flow of pressurized liquid from the accumulator to the motor. When the normally-closed control valve is opened, pressurized liquid flows from the.

accumulator to the motor to cause the motor to produce a circuit-breaker-elosing operation. When the circuitbreaker-closing operation is completed, the control valve is operated to its closed position. This valve-closing ction not only interrupts communication between the accumulator and the motor but also quickly relieves the pressure in the motor, so that if the breaker had been closed on a fault, it can reopen immediately after closing without significant interference from the motor. It" the breaker opening operation were to take place at some later instant, instead of immediately upon closing, the fluid motor likewise would offer no significant opposition to breaker-opening since closing of the control valve would have already relieved the pressure in the motor.

In certain circuit breaker applications, it is important to reclose the circuit breaker within a very short time interval after the breaker is initially tripped to open. In the usual hydraulically-operated circuit breaker referred to hereinabove, reclosing is el'leced by opening the control valve to cause pressurized liquid to flow from the accumulator to the fluid motor to initiate another breakerclosing operation. To lessen the time required for reclosing, it is customary to open this control valve well ahead of the instant at whicn the breaker would ordinarily have reached its fully-open position so that motion of the breaker can be reversed even before the breaker has reached the fully-open position.

I have found, however, that in most hydraulicallyopcrated systems, the fluid motor does not begin to produce breaker-closing immediately after the control valve is opened. Although accumulator pressure becomes available to resist brcakercpening operation immediately upon opening of the control valve, breaker-opening continues for several electrical cycles after the control valve is opened; and this unduly lengths the time interval required for rcclosing.

Accordingly, an object of my invention is to lessen the time interval required for a hydraulically-actuated' operating mechanism to produce reclosing of a circuit breaker.

Another object is to lessen this reclosing time interval by reducing the period of time required for reversing the operation of the fluid motor after the control valve between the fluid motor and the accumulator is opened.

Another object is to achieve these reductions in reclosing time without impairing the ability of the circuit breaker to open at the desired high speed if closed on a faulted power line.

In carrying out my invention in one form, I provide between the above-described control valve and accumulator, a check valve that offers little resistance to flow from the accumulator toward the fluid motor but a much greater "ice resistance to fiow from the motor toward the accumulator. When the control valve is opened to initiate a normal closing operation, flow is from the accumulator to the motor; and the check valve, being of low resistance to flow in this direction, does not significantly interfere. When the control valve is closed at the end of the circuitbreaker-closing operation to interrupt communication between the accumulator and the motor and to vent the motor, the check valve likewise offers no interference since it is outside of the hydraulic path through which venting takes place. When the control valve is opened during a circuit-breaker-closing operation to initiate a circuit breaker reclosing operation, there is a tendency for pressurized liquid to flow from the motor toward the accumulator, and it is then that the high resistance offered by the check valve to such reverse flow comes into action. This high resistance creates a pressure behind the check valve, and hence in the fluid motor, that materially exceeds the accumulator pressure and is maintained at a level above the accumulator pressure until opening motion of the breaker is terminated. Maintaining this overpressure for this extended interval quickly dece'lerates the then-opening circuit breaker, shortening its opening stroke both in length and in time, and thus shortening the time required for the fluid motor to become effective to reverse motion of the breaker and eventually complete the reclosing operation.

For a better understanding of my invention, referonce may be had to the following description taken in conjunction with the accompanying drawings, wherein:

FIG. 1 shows a circuit breaker operating mechanism embodying one form of my invention. The circuit breaker is shown in its fully-open position.

FIG. 2 shows the operating mechanism of FIG. 1 in a position through which it passes during a closing operation immediately before the contacts of the breaker first touch.

FIG. 3 shows a portion of the circuit breaker when it is in its fully-closed position.

FIG. 4 shows the circuit breaker operating mechanism in an intermediate position through which it passes during an opening operation. At the instant depicted, the control valve of the mechanism has been opened to initiate circuit breaker reclosing, but reverse motion of the circuit'breaker has not yet begun.

FIG. 5 is a graphic representation of certain relationships that are present in the illustrated operating mechanism and also in a corresponding mechanism without the check valve of my invention.

FIG. 6 is an enlarged sectional view taken along the line 6-6 of FIG. 1.

FIG. 7 is an enlarged sectional view similar to FIG. 1 but showing a modified form of the invention.

Referring now to the drawings, there is shown a circuit breaker l0 comprisinga set of separable contacts 12 and 14 for controlling apower circuit 16. The contacts 12 are stationary contacts and the contact 14 is a movable contact that is biased by means of a suitable opening spring 17 in a direction away from the stationary contacts 12. The movable contact 14 is arranged to be driven from its open position of FIG. 1 through its intermediate position of FIG. 2 into its closed position of FIG. 3 against the bias of spring 17 to close the power circuit 16. Reverse movement of the contacts 14 from the closed position of FIG. 3 toward the position of FIG. 1 under theinfiuence of operating spring 17 interrupts the flow of current through the circuit 16. 7

Power for driving'the contact 14-into its closed position of FIG. 3 is derived from a liquid motor 20 having a piston 22 that is coupled to the movable contact 14 through a linkage generally indicated at 23. This linkage 23, which has been shown in simplified form to facilitate an understanding of the present invention, comprises a piston rod 24, a pivoted lever 25, and a reciprocable operating rod 26. The lever 25 is pivotally mounted at one end on a stationary pivot 27 and is pivotally connected at its outer end to the operating rod 26. The piston rod 24 is pivotally connected to the lever 25 at a point spaced from the pivot 27 and is capable of transmitting clockwise closing motion to the lever 25 when the piston 22 of the hydraulic motor is driven downwardly during a circuit breaker closing operation. Such clockwise motion of lever drives the operating rod 26 downward, and such downward motion forces the movable contact 14 into closing engagement with the stationary contacts 12 while compressing the opening spring 17.

When the closed position of FIG. 3 is reached, a compression spring 29 forces a conventional latch 28 into place behind a roller 28a carried by the lever 25. The latch 28, which is mounted on a pivot 2%, serves to hold the contact 14 closed against the bias of opening spring 17 after the closing stroke has been completed. Breaker opening is effected simply by driving the latch in a counterclockwise direction off the top of roller 28a to remove the restraint of the latch and allow the contact 14 to be driven out of engagement with the contacts 12 by means of the opening spring 17.

For producing downward circuit-breaker-closing motion of the piston 22 of the hydraulic motor 20, pressurized liquid is supplied to the upper side of the piston 22 from a pneumo-hydraulic accumulator 30 via a supply line 32a, 32b. This accumulator 30 may be of any suitable conventional design and in the disclosed embodiment contains a pocket of highly pressurized gas trapped above a supply of liquid contained within the accumulator. The accumulator is maintained in a charged, or pressurized, condition by means of a suitable pump 31 which forces liquid from a sump 31a into the accumulator whenever pressure in the accumulator falls below a predetermined level, preferably about 2800 p.s.i. A suitable pressure-sensitive cut-off switch terminates operation of the pump when the accumulator pressure reaches a value of about 3000 p.s.i.

The flow of pressurized liquid from the accumulator 30 to the motor 20 is controlled by valve means 32 disposed between the accumulator and the motor in the sup ply line 32a, 32b. Since the details of this valve means 32 are not my invention and are disclosed and claimed in appl. S.N. 856,122, Coggeshall et al., filed November 30, 1959, now Patent No. 2,972,337, and assigned to the assignee of present invention, they will be described only in sufficient detail to provide an understanding of the present invention. This valve means 32 compromises an inlet port 34 interconnecting the accumulator and the motor 20, and a dump port 36, interconnecting the motor 20 and the low pressure sump 31a, which is at atmospheric pressure. The flow of liquid through these ports is controlled by poppet valve member 38 that is movable between the closed position of FIG. 1 and the fully-open position of FIG. 2. In the closed position of FIG. 1, the valve member 38 abuts against a valve seat 35 surrounding the inlet port 34, thus closing the inlet port 34 and thereby blocking communication between the accumulator 3t) and the motor 20, while permitting free communication between the motor 20 and the sump 31a through the dump port 36. In the fully-open position of FIG. 2, the valve member 38 closes the dump port 36 and allows free communication between the accumulator 30 and the motor 20 through the inlet port 34.

On the accumulator side of the valve member 38 there is a chamber 40 that freely communicates with the ac cumulator 30 and is normally filled with pressurized liquid from the accumulator 30. This pressurized liquid exerts a force directly on the valve member 38 tending to drive the valve member 33 upwardly out of its closed position of FIG. 1. But this opening force is overbalanced by the force that the pressurized liquid in chamber 40 exerts on a balancing piston 42 fixed to the valve member 38 through a piston rod 43 integral with the valve member 38 and the piston 42. As is evidenced by the slightly enlarged bore of the chamber 40 that receives piston 42, the piston 42 has an effective working face slightly larger than the area of the valve member 38 bounded by the seat 35 of inlet port 34, and thus the pressurized liquid in chamber 40 exerts a net force on the valve member 38 tending to hold it in the closed position of FIG. 1. In the disclosed valve, the difference in these total areas is rather small so that the net force holding the valve member 38 closed is correspondingly small, The region of the valve immediately beneath the piston 42 is always freely vented to the sump 31a, and thus the liquid in this region plays no significant part in the force relationships described immediately above.

Valve-opening operation is controlled by means of an actuating piston disposed immediately beneath the piston rod 43 of the valve member 38. This actuating piston 50 is separate from the valve member 38 but bears against the lowermost face of the piston rod 43 and is capable of transmitting upward motion to the valve member 38 through the piston rod 43. Such upward motion of the actuating piston 50 is produced by supplying pressurized liquid to the space 52 beneath the piston 50 from the accumulator 30. This pressurized liquid quickly overcomes the above-described net force holding the valve member 38 closed, and thus forces the piston 50 together with the valve member 38 upwardly. Since the net force holding the valve member 38 closed is relatively small, as was explained hereinabove, a relatively small actuating piston (50) can be used for overcoming the net closing force. This means that only a relatively small volume of pressurized liquid need be supplied to the actuating piston 50 to enable it to overcome the net closing force and thereby effect valve-opening.

For controlling the flow of liquid to and from the space 52 beneath the actuating piston 50, a three-way pilot valve 54 is provided in a line 55 leading from the accumulator 30 to the space 52. This pilot valve 54 comprises an inlet port 56 interconnecting the accumulator 30 and the space 52 beneath the actuating piston 50 and a dump port 58 interconnecting the space 52 and the low pressure sump 31a, and a movable pilot valve member 60 for controlling flow through these pilot valve ports 56 and 58. When the pilot valve member 60 is in its lower position of FIG. 1, it blocks the flow of liquid through the inlet port 56 but permits free communication between the chamber 52 and the sump 31a through the dump port 58. When the pilot valve member 60 is in its upper po sition of FIG. 2, it closes the dump port 58 to seal off the sump 31a from the chamber 52 but allows free communication between the accumulator 30 and the chamber 52 through the inlet port 56.

For providing a force to bias the pilot valve closed under normal conditions a small piston 62 is fixed to the valve member 60 through an integral piston rod 64. This piston 62 is disposed at the lower end of a chamber 66 communicating with the accumulator 30 so that full pressure from the accumulator normally acts on its upper surface. As will be apparent from the slight enlargement at the lower end of chamber 66, this piston 62 has an effective working face slightly larger than the area of the valve member 60 bounded by the inlet port 56, and thus the pressurized fluid in the chamber 66 provides a net force biasing the pilot valve member 60 closed.

For overcoming this net closing force on the pilot valve member 60 so as to effect opening of the pilot valve, a solenoid schematically indicated at 70 is provided. This solenoid 70 is controlled by means of control circuits 72 and 74 generally corresponding to those shown and claimed in US. Patent 2,381,336Coggeshall, and reference may be had to such patent for a more detailed description of such circuits. Such circuits 72 and 74 are shown in simplified, schematic form in the present application to facilitate an understanding of the present invention. Referring now to the solenoid 70, it will be noted that the solenoid has an armature 75 mechanically connected to the pilot valve member 60 through a pilot valve operating rod 76, and also has a coil 77 connected in the control circuit 72. This control circuit 72 extends from positive to negative terminals of a suitable control power source and contains a manually-operable closing-control switch 79 connected in series with the solenoid coil 77 and a suitable anti-pump device 80 of conventional design such as shown in the Coggeshal'l patent for preventing inadvertent repetitive closing operations. When the switch 79 is closed, the coil 77 is energized through the circuit 72 and responds by lifting its armature 75 and the pilot valve member 60 to open the pilot valve against the opposition of the previously-described net force holding the pilot valve closed. The anti-pump device 80 opens the energizing circuit 72 immediately after the solenoid has opened the pilot valve and maintains this circuit open so long as the closing control switch 79 is held closed. By opening the circuit 72 before the motor has completed a breaker closing operation, no significant flux from the coil 77 is available to interfere with return motion of the armature 75 at the end of the breaker-closing operation.

The armature 75 is held in its upper position until the circuit-breaker-closing operation can be completed by means of a permanent magnet 81 provided above the armature 75. This permanent magnet 81 has insufiicient strength to lift the armature 75 from its lower position but is sufficiently strong to hold the armature in its elevated position once moved into such position. At the end of the circuit-breaker-closing stroke, the normally open switch 82 is closed by suitable means sensitive to the position of the breaker. Closing of this normally-open switch82 completes a pilot valve closing circuit 74. This circuit '74 contains a flux-neutralizing winding 84 capable when energized of quickly neutralizing the holding flux of the permanent magnet 81. Thus, when the breaker 10 reaches closed position, the switch 82 is closed to complete the circuit 74 to cause the winding 84 to effect release of the armature 75 from the permanent magnet 81, thereby allowing a small spring 86 to return the pilot valve to its closed position.

When the pilot valve member 60 returns to its closed position, it blocks the inlet port 56 and opens the dump port 58 thereby relieving the pressure in the space 52 beneath the actuating piston 59. This allows the pressurized liquid acting. against the upper surface of the piston 42 of the main controlling valve to return the valve member 38 from the position of FIG. 2 to its position of FIG. 1. As soon as the main valve member 38 begins leaving the dump port 36, it begins relieving the pressure in the cylinder of the fluid motor 20. When the valve member 38 reaches its position of FIG. 1, it blocks the inlet port 34 and thus blocks the further flow of pressurized liquid through this port 34. Pressure above the piston 22 is completely relieved within a very short time after the dump port 36 is first opened.

A circuit breaker closing operation would be initiated by closing the control switch 79 to cause the solenoid 79 to lift the pilot valve member 64 from its position of FIG. 1. Such upward movement of the pilot valve member 60' would permit liquid to flow at high speed from the accumulator through the line 55 and the pilot valve inlet port 56 into the chamber 52 beneath the actuating piston 5t) of the main control valve. This pressurized liquid in the chamber 52 would force the piston upwardly, and the piston 50, in so moving, would drive the main valve member 38 from the position of FIG. 1 to that of FIG. 2. Pressurized liquid would then flow from the accumulator 30 into the cylinder of the fluid motor through the inlet port 34. This liquid would quickly force the motor piston 22 downwardly against a reset spring 87, thereby effectively driving the contacts into the closed position of FIG. 2.

If a breaker is closed on a faulted power line, it must be capable of reopening within a very short time, e.g. see, after its contacts first touch. If it be assumed that a fault were present on the power line 16 at the time the breaker contacts touched at the end of the above-described closing operation, heavy current would immediately flow through the circuit 16, energizing a conventional overcurrent relay 9h through a current transformer 91; The relay would respond to such energization by closing its normally-open contacts 92, thereby completing a tripping circuit for a conventional tripping solenoid 94. This tripping solenoid 94 would respond by forcing the latch 28 counterclockwise about its pivot 29a thereby allowing the breaker to be opened by the opening spring 17 without further restraint from the latch 28.

At the same time that latch-tripping occurs, the control switch 82 is closed, releasing the armature 74 of the pilot valve solenoid, and allowing the spring 86 to reclose the pilot valve. In reclosing, the pilot valve member 6i) relieves the pressure in the actuating chamber 52 through the pilot valve dump port 58, thereby allowing the main valve member 38 to return to its position of FIG. 1 under the influence of the pressurized liquid acting on the upper face of valve controlling piston 42. Movement of the valve member out of its position of FIG. 2 can be initiated and can take place at an extremely high speed because the amount of liquid required to be vented from the chamber 52 is exceptionally small, as has been described hereinabove. High speed movement of the valve member out of its position of FIG. 2 effects high speed relief of the pressure above the main piston 22, thus allowing the reset spring 87 beneath the piston 22 and the main opening spring 17 to drive the piston upwardly without significant restraint from the liquid above the piston 22.

In the absence of any significant restaint from liquid above the piston-22 and from the trip latch 28, the breaker can quickly reopen to interrupt the current flowing through the contacts 12, 14. In a hydraulically-operated circuit breaker constructed generally as shown, times between contact-make and contact-part Well within of a second have consistently been achieved.

As shown in FIGS. 1 and 2, a suitable buffer 96 is provided beneath the actuating piston 59 to prevent the valve seat 35 from being damaged by impact resulting from engagement between the movable valve member 33 and the valve seat 35 upon closing of the valve member 33. This buffer retards the valve member 38 near the end of its closing stroke to reduce the severity of this impact. It is to be noted that the valve means 32 shown in the drawings contains a spring 25 urging the main valve member 38 into its closed position of FIG. 1. This is a light spring which is intended to assure that the valve member 38 is correctly positioned when the system is initially filled with pressurized liquid. The hereinabove-described operation of valve member 33 is not materially affected by this light spring95 once the system is pressurized.

In certain circuit breaker application, it is important to reclose the breaker within a very short time after the breaker is initially tripped to open. In the disclosed circuit breaker, reclosing is effected by opening the control valve 32 to supply pressurized liquid from the accumulator tothe top of piston 22 of the fluid motor to initiate another breaker-closing operation. The control valve 32 is opened well ahead of the instant at which the breaker would ordinarily reach its fully-open position of FIG. 1 so that motion of the breaker can be reversed even before the breaker reaches its fully-open position. For initiating such an opening operation of the control valve 32 at the desired point in an opening stroke, a biase -open switch 1% is provided. This biased-open switch ii'ti) comprises a movable switch member 1531 that is held open whenthe circuit breaker is closed by a suitable spring and is moved into its closed position after a predetermined portion of the circuit-breaker-opening stroke by a suitable cam 102 fixed to the circuit breaker operating rod 26. This biased-open switch 106 is connected in series with the coil 77 of the closing solenoid and in series with a selector switch 104 that is closed either manually or by suitable control means (not shown) when it is desired to set the breaker for automatic reclosing.

When the breaker is tripped from its closed position of FIG. 3, as by releasing the latch 28 in response to an overcurrent condition in power line 16, the main contact 14 of the breaker moves upwardly toward its fullyopen position. After a predetermined amount of such upward opening movement, the cam 102 on the breaker operating rod 26 drives the movable contacts 161 of the reclosure-initiating switch 108 closed, completing an energizing circuit for the solenoid 75. This circuit extends from the positive terminal of a source of control power, through selector switch 1434, reclosing switch 100, the solenoid winding 77 and the anti-pump device 80 to the negative terminal of the control power source. When this circuit is completed, the energized solenoid 75 responds by lifting the pilot-valve operating rod 76 and the pilot valve 60 to supply pressurized liquid to the space beneath piston 50, which is then in its lowermost position. The piston 50 is accordingly driven upwardly to move the control valve member 38 from its dotted line position of FIG. 4 into its solid line position. The parts of the operating mechanism at this instant are depicted in FIG. 4, where the circuit breaker is shown traveling through an intermediate position toward its fully-open position. Movement of the control valve member 38 into its solid line position of FIG. 4 blocks the venting port 36 and establishes communication between the accumulator 30 and the motor 20. After a short transient period (soon to be described) pressurized liquid from the accumulator flows into the motor space above the piston 22 to reverse the direction of piston 22 and drive it downwardly into its circuit-breaker-closed position.

To aid in decelerating the circuit breaker and the piston 22 as they move together toward open position, I provide means including a check valve 120 located between the control valve 32 and the accumulator 30. This check valve 120 comprises a movable valve member 122 that is slidable within an enlarged portion of duct 32a between a first position, where it is shown in FIG. 1, and a second position, where it is shown in FIG. 4. In its position of FIG. 1, movable check valve member 122 abuts near its outer periphery against an annular shoulder 125 projecting inwardly from the walls of duct 32a. As will be apparent from FIG. 6, the movable check valve member 122 includes a central hub 128 and circurneferentially-spaced ribs 126 projecting radially-outward from the central hub 128 to provide large flow passages between adjacent ribs 126. When the movable check valve member 122 is in its position of FIG. 1, pressurized liquid is free to flow through these flow passages between the ribs from the accumulator 30 toward the fluid motor 20. During an ordinary circuit-breaker-closing operation, such as depicted in FIG. 2, the liquid flowing from the accumulator 30 to the motor 20 in response to opening of the control valve 32 simply forces the movable check valve member 122 into its position of FIG. 1, and liquid flows freely past the check valve through the passages between its ribs 126.

When the breaker reaches the end of its closing stroke and the control valve 32 is then moved into closed position, as was described above, the movable check valve member 122 remains in its position of FIG. 2 since there is no pressure diiferential available to drive it out of this position. The check valve member 122 does not interfere with the desired venting of motor 20 that occurs upon closing of the control valve 32 since such venting takes place through the venting passage constituted by the duct 32b and the exhaust port 36. The check valve 120 being remote from this venting passage, offers no opposition to the desired venting of motor 20.

When the movable check valve member 122 is in'its position of FIG. 4, the flow passages between ribs 126 are blocked by the conical seat 130 against which the movable check valve member 122 abuts. Pressurized liquid is therefore prevented from flowing through these relatively large passages toward the accumulator 30. It is only through a restricted central passage 132 formed in the movable check valve member 122 that liquid can flow toward the accumulator 30 when the check valve member 122 is in its position of FIG. 4.

The manner in which the check valve 120 acts during a circuit breaker reclosing operation will now be described. Assume that the circuit breaker is moving toward open position and that the movable control valve member 38 of the control valve 32 is driven from its dotted line position of FIG. 4 into its solid line position. As was described hereinabove, upon closing of the main exhaust port 36, the liquid leaving the motor 20 through the duct 32b will be diverted through the passageway 34 into the duct 32a, as indicated by the arrow 134. This liquid will quickly force the movable check valve member 122 into its position of FIG. 4, thus leaving only the restricted central passageway 132 for liquid to flow past the movable check valve member 122 toward the accumulator 30.

The efiect of introducing this severe restriction to flow in the direction of arrow 134 is to raise the pressure ahead of the upwardly moving piston 122, i.e., the back pressure, to a value materially higher than the accumulator pressure and to maintain this back pressure ahead of the piston 22 at a level higher than the accumulator pressure for substantially the entire period during which the piston 22 continues to move toward open position after the control valve 32 is opened. This relationship is graphically depicted in FIG. 5, where the back pressure ahead of piston 22 is depicted in the lower solid line curve A. The control valve 32 is closed at about 3.5 cycles after the breaker is tripped, and in response to closing of the control valve 32, the pressure ahead of the piston 22 quickly builds up to about percent of the accumulator pres sure. The pressure ahead of piston 22 remains in this general range for about 2 cycles and then gradually falls to a value equaling the accumulator pressure. During substantially the entire period extending from the instant F that pressure ahead of piston 22 first exceeded the accumulator pressure until movement of the piston in an opening direction was (about 3 /2 cycles) terminated, the pressure ahead of piston 22 was above the pressure of the accumulator. This will become more readily apparent if reference is also had to the solid line upper curve A, which shows opening movement of the piston 22 terminating at about the instant E. From the instant F when the pressure ahead of the piston 22 first exceeded the accumulator pressure to the instant E, the pressure ahead of the piston 22 exceeds accumulator pressure, as is evident from curve A.

Quickly establishing this high back pressure ahead of the piston 22 and maintaining it for this extended period (1.e. until opening motion of the circuit breaker is terminated) results in decelerating the upwardly-moving piston 22 more quickly than could be done without the check valve (120). This more rapid deceleration not only terminates the opening stroke more quickly than would be the case without the check valve but also shortens the opening stroke. These two factors combine to produce a significant reduction in the total time required to return the movable contact to its closed position. That the opening stroke with the check valve present is shorter, both in time and length, will be apparent from a comparison of travel curve A with the travel curve B, which depicts travel of the piston 22 in an operating system corresponding to that disclosed but without the check valve. This comparison shows that with the check valve, the piston 22 travels through a shorter opening stroke than without the check valve and also reaches the limit of its opening travel at an. instant E ahead of the instant G at which the piston without the check valve reaches the limit of its opening stroke. These two factors enable the motor 20 to return the movable contact 14 to its closed position at an instant K approximately 2 cycles ahead of the instant L at which contactmake would otherwise have occurred.

Without the check valve present between the accumulator 30 and the control valve 32, closing of the control valve would result in the pressure ahead of the piston varying in the approximate manner depicted in curve B of FIG. 5. This curve B shows that the pressure ahead of the piston 22 quickly builds up to approximately the same value as with the check valve but instead of being maintained at this elevated level for an extended period, quickly falls and then oscillates about a pressure value corresponding to accumulator pressure. Thus, in an operating system having no check valve, the pressure is not maintained above the accumulator pressure during the critical interval extending from the instant F to the instant (G) at which opening motion is terminated. The result is a longer opening stroke, more time needed to terminate the opening stroke, and, hence, more total time required for reclosing.

It is to be noted that the check valve 120 does not raise the peak pressure developed ahead of the piston appreciably above the peak pressure developed without the check valve but merely maintains this peak pressure for a much longer interval than is the case without the check valve. Since the peak pressure developed'with the check valve is not appreciably higher than that developed without the check valve, it will be apparent that inclusion of the check valve does not require that the system with the check valve be designed to have appreciably greater mechanical strength than without the check valve.

The peak value of the pressure ahead of the piston 22 depends upon the size of restriction 132 in the movable check valve member 122. Generally speaking, the smaller the minimum cross-sectional area of this restriction 132, the higher will be this peak pressure, and the higher will be the mean efiective back pressure. In apreferred form of my invention, this restriction is of such a size that the peak pressure developed is not appreciably higher than the peak pressure that would be developed without the check valve. This preferred embodiment is the embodiment illustrated in the graph of FIG. 5.

In certain applications, it may be desirable to maintain the back pressure near its peak value for an even longer period than is depicted in curve A of FIG. 5. Referring to FIG. 7, this can be accomplished by providing the restricted passage 132 with a pressure-sensitive valve that is normally maintained in its closed position of FIG. 7 by means of a suitable compression spring 152. This compression spring acts between the movable check valve member 122 and a perforated shoulder 154 carried at one end of a valve rod 155 extending through the passage 132. When the movable check valve member 122 is driven into its position of FIG. 4 during a breaker-reclosing operation, the pressure sensitive valve 150 remains closed until the pressure on opposite sides of the checkvalve member 122 exceeds a predetermined value, at which time the valve 150 moves to the right to open the restricted passage 132. When the pressure differential begins to drop below this predetermined value, the valve 150 closes under the bias of spring 152 and thus tends to increase the back pressure to the left of the check valve member 122. This action serves to maintain the pressure differential at the desired high value for an even longer interval than is depicted in curve A.

Although the illustrated embodiment of my invention includes a linkage (23) of the type that is not mechanically-trip-free, it is to be understood that the invention is also applicable to those mechanisms which include suitable mechanically-trip-free linkages. An example of such a linkage is shown and claimed in my application SN.

3,964, filed January 21, 1960, noW Patent No. 3,009,034, and assigned to the assignee of the present invention. In such a trip-free mechanism, after a tripping operation occurs, the mechanism must be reset to a force-transmitting condition before it is again capable of transmitting closing thrust to the movable contact 14'. Opening of the control valve 32 to initiate a reclosing operationmust therefore be delayed until the linkage is reset to a thrusttransmitting condition. Such resetting operation requires a definite amount of time after tripping is initiated, thus requring that attempted reclosure be initiated only after this time interval has elapsed. A particular advantage of my invention when applied to such a mechanism is that I can reverse thedirection of motion of the circuit breaker and the piston 22 from opening to closing within an exceptionally short time after the linkage-resetting operation has been completed.

Another advantage of my disclosed arrangement is that I can provide the supply portion of my hydraulic system with a sensitive pressure-relief valve that is not subject to false operation from the surge pressures occurring when the valve member 38 of the control valve 32 is driven into its open position to initiate a reclosing operation. In this regard, I provide a relief valve 160 of suitable conventional structure in the supply line 32a between the check valve and the accumulator 30. This relief valve is set to open at a pressure several hundred p.s.i. above the 3000 psi. pressure at which the accumulator is normally maintained and in this way protects the accumulator from pressures above this level (at which the relief valve is set). Such a relief valve would not be operated by the transient overpressures depicted in curve A because these overpressures exist only on the other side of the check valve 120, i'.e., between the check valve 120 and the fluid motor 20.

While I have shown and described a particular embodiment of my invention it will be obvious to those skilled in the art that various changes and modifications may be made without departing from my invention in its broader aspects, and I, therefore, intend in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In a hydraulically-controlled operating system for an electric circuit breaker, a fluid motor comprising a movable piston adapted to move in a closing direction to close said circuit breaker and adapted to move in a reverse direction during opening of said circuit breaker, an accumulator for supplying pressurized operating liquid to said motor, a dump port interconnecting said motor and a low pressure region, control valve means located hydraulically between said accumulator and said motor for controlling the flow of pressurized liquid to and from said motor, said control valve means beingeiiective in a first condition to aiford communication between said accumulator and said motor and to close said dump port and being effective in a second condition to block communication between said motor and said accumulator and to afford communication between said motor and said low pressure region through said dump port, means for operating said control valve means into said first condition to produce movement of said piston in said closing direction and for operating said control valve means into said second condition to permit movement of said piston in said reverse direction, means for restoring said control valve means to said first condition during movement of said piston in said reverse direction to initiate a circuitbreaker-reclosing operation, decelerating means for producing ahead of said piston during movement in said reverse direction occurring after said control valve means has been restored to said first condition a substantially higher back pressure than the pressure then present in said accumulator and for maintaining said back pressure above the accumulator pressure during substantially the entire interval extending from the instant that said back pressure first exceeds said accumulator pressure until movement of said piston in said reverse direction is terminated, said decelerating means comprising a check valve located hydraulically between said control valve means and said accumulator for restricting the flow of liquid into said accumulator from said fiuid motor during movement of said piston in said reverse direction, said check valve offering a substantially greater resistance to flow from said motor toward said accumulator than to flow from said accumulator toward said motor, said hydraulic system being so constructed that said accumulator and other system components can safely withstand the maximum pressures developed in said system even in the absence of said check valve.

2. In a hydraulically-controlled operating system for an electric circuit breaker, a fluid motor comprising a movable piston adapted to move in a closing direction to close said circuit breaker and adapted to move in a reverse direction during opening of said circuit breaker, an accumulator for supplying pressurized operating liquid to said motor, a dump port interconnecting said motor and a low pressure region, control valve means located hydraulically between said accumulator and said motor for controlling the flow of pressurized liquid to and from said motor, said control valve means being etlective in a first condition to afford communication between said accumulator and said motor and to close said dump port and being eflective in a second condition to block communication between said motor and said accumulator and to afford communication between said motor and said low pressure region through said dump port, means for operating said control valve means into said first condition to produce movement of said piston in said closing direction and for operating said control valve means into said second condition to permit movement of said piston in said reverse direction, means for restoring said control valve means to said first condition during movement of said piston in said reverse direction to initiate a circuitbreaker-reclosing operation, decelerating means for producing ahead of said piston after said control valve means has been restored to said first condition a sustained back pressure exceeding the pressure then present in said accumulator, said decelerating means comprising a check valve located hydraulically between said control valve means and said accumulator for restricting the flow of liquid into said accumulator from said fluid motor during movement of said piston in said reverse direction, said check valve oflering a substantially greater resistance to flow from said motor toward said accumulator than to flow from said accumulator toward said motor, said hydraulic operating system being so constructed that said accumulator and other system components can safely withstand the maximum pressures developed in said system even in the absence of said check valve.

3. The operating system of claim 2 in which said check valve comprises a movable check valve member having a first position into which it is driven by liquid flowing toward said accumulator and a second position into which it is driven by liquid flowing away from said accumulator, said check valve having a substantially greater resistance to flow toward said accumulator when said movable check valve member is in said first position than its resistance to flow away from said accumulator when said movable check valve member is in said second position.

4. The operating system of claim 2 in which said check valve comprises a movable check valve member having a first position into which it is driven by liquid flowing toward said accumulator and a second position into which it is driven by liquid flowing away from said accumulator, said check valve having a substantially greater resistance to flow toward said accumulator when said movable check valve member is in said first position than its resistance to flow away from said accumulator when said movable check valve member is in said second position,

said movable check valve member containing at least one restricted passage therethrough affording communication between said motor and said accumulator when said check valve member is in said first position for limiting the peak back pressure developed ahead of said piston when said check valve member is in said first position.

5. The system of claim 4 in which said restricted passage is of such a cross-sectional area that the peak back pressure developed with said check valve present approximately equals the peak back pressure that would be de- Veloped without a check valve.

6. The operating system of claim 2 in combination with a pressure relief valve for protecting said accumulator from overpressure, said relief valve being located by draulically between said accumulator and said check valve and being set to provide pressure relief at a value of pressure exceeding the maximum normal pressure in said accumulator but below the transient peak pressure developed between said check valve and said motor upon operation of said control valve means into said first condition to initiate circuit-breaker-reclosing.

7. The operating system of claim 2 in which said check valve comprises a movable valve member having a first position into which it is driven by liquid flowing toward said accumulator and a second position into which it is driven by liquid flowing away from said accumulator, said check valve having a substantially greater resistance to flow toward said accumulator when said movable check valve member is in said first position than its resistance to flow away from said accumulator when said movable check valve member is in said second position, said movable check valve member'containing at least one restricted passage therethrough affording communication between said motor and said accumulator when said check valve member is in said second position for limiting the peak back pressure developed ahead of said piston when said check valve member is in said second position, and pressure-sensitive valve means for permitting substantial flow through said restricted passage toward said accumulator only when said back pressure exceeds the accumulator pressure by a predetermined amount.

8. In a hydraulically-controlled operating system for an electric circuit breaker, a fluid motor comprising a movable piston adapted to move in a closing direction to close said circuit breaker and adapted to move in a reverse direction during opening of said circuit breaker, an accumulator for supplying pressurized operating liquid to said motor, a control valve for controlling the flow of pressurized operating liquid from said accumulator to said motor; said control valve comprising an inlet port interconnecting said accumulator and said motor, a dump port interconnecting said motor and a low pressure region, and a valve member movable between a closed position in which it seals 06? said inlet port and an open position in which it seals oif said dump port; said dump port being open when said valve member is in its closed position and said inlet port being open when said valve member is in its open position, means for moving said valve member into said open position to produce movement of said piston in said closing direction and for moving said valve member into said closed position to permit movement of said piston in said reverse direction, means for returning said valve member to said open position during movement of said piston in said reverse direction to initiate a circuit-breaker-reclosing operation, decelerating means for producing ahead of said piston during movement in said reverse direction occurring after said valve member has been returned to said open position a substantially higher back pressure than the pressure then present in said accumulator and for maintaining said back pressure above the accumulator pressure during substantially the entire interval extending from the instant that said back pressure first exceeds said accumulator pressure until movement in said reverse direction of said piston is terminated, said decelerating means comprising a 13 check valve located hydraulically between said control valve and said accumulator for restricting the flow of liquid into said accumulator from said fluid motor during movement of said piston in said reverse direction, said check valve ofiering a substantially greater resistance to flow from said motor toward said accumulator than to flow from said accumulator toward said motor, said hydraulic operating system being so constructed that said accumulator and other system components can safely Withstand the maximum pressures developed in said sys- 10 tem even in the absence of said check valve.

References Cited in the file of this patent UNITED STATES PATENTS 1,983,051 Smith Dec. 4, 1934 14 Tyler May 19, Eaton Nov. 12, Umphrey Nov. 10, Umphrey Dec. 8, Peek Feb. 28, Beatty et al. Apr. 3, Perry et al. Oct. 2, Barkan Jan. 12, Coggeshall et al Feb. 21,

FOREIGN PATENTS Great Britain Feb. 9, 

1. IN A HYDRAULICALLY-CONTROLLED OPERATING SYSTEM FOR AN ELECTRIC CIRCUIT BREAKER, A FLUID MOTOR COMPRISING A MOVABLE PISTON ADAPTED TO MOVE IN A CLOSING DIRECTION TO CLOSE SAID CIRCUIT BREAKER AND ADAPTED TO MOVE IN A REVERSE DIRECTION DURING OPENING OF SAID CIRCUIT BREAKER, AN ACCUMULATOR FOR SUPPLYING PRESSURIZED OPERATING LIQUID TO SAID MOTOR, A DUMP PORT INTERCONNECTING SAID MOTOR AND A LOW PRESSURE REGION, CONTROL VALVE MEANS LOCATED HYDRAULICALLY BETWEEN SAID ACCUMULATOR AND SAID MOTOR FOR CONTROLLING THE FLOW OF PRESSURIZED LIQUID TO AND FROM SAID MOTOR, SAID CONTROL VALVE MEANS BEING EFFECTIVE IN A FIRST CONDITION TO AFFORD COMMUNICATION BETWEEN SAID ACCUMULATOR AND SAID MOTOR AND TO CLOSE SAID DUMP PORT AND BEING EFFECTIVE IN A SECOND CONDITION TO BLOCK COMMUNICATION BETWEEN SAID MOTOR AND SAID ACCUMULATOR AND TO AFFORD COMMUNICATION BETWEEN SAID MOTOR AND SAID LOW PRESSURE REGION THROUGH SAID DUMP PORT, MEANS FOR OPERATING SAID CONTROL VALVE MEANS INTO SAID FIRST CONDITION TO PRODUCE MOVEMENT OF SAID PISTON IN SAID CLOSING DIRECTION AND FOR OPERATING SAID CONTROL VALVE MEANS INTO SAID SECOND CONDITION TO PERMIT MOVEMENT OF SAID PISTON IN SAID REVERSE DIRECTION, MEANS FOR RESTORING SAID CONTROL VALVE MEANS TO SAID FIRST CONDITION DURING MOVEMENT OF SAID PISTON IN SAID REVERSE DIRECTION TO INITIATE A CIRCUITBREAKER-RECLOSING OPERATION, DECELERATING MEANS FOR PRODUCING AHEAD OF SAID PISTON DURING MOVEMENT IN SAID REVERSE DIRECTION OCCURING AFTER SAID CONTROL VALVE MEANS HAS BEEN RESTORED TO SAID FIRST CONDITION A SUBSTANTIALLY HIGHER BACK PRESSURE THAN THE PRESSURE THEN PRESENT IN SAID ACCUMULATOR AND FOR MAINTAINING SAID BACK PRESSURE ABOVE THE ACCUMULATOR PRESSURE DURING SUBSTANTIALLY THE ENTIRE INTERVAL EXTENDING FROM THE INSTANT THAT SAID BACK PRESSURE FIRST EXCEEDS SAID ACCUMULATOR PRESSURE UNTIL MOVEMENT OF SAID PISTON IN SAID REVERSE DIRECTION IS TERMINATED, SAID DECELERATING MEANS COMPRISING A CHECK VALVE LOCATED HYDRAULICALLY BETWEEN SAID CONTROL VALVE MEANS AND SAID ACCUMULATOR FOR RESTRICTING THE FLOW OF LIQUID INTO SAID ACCUMULATOR FROM SAID FLUID MOTOR DURING MOVEMENT OF SAID PISTON IN SAID REVERSE DIRECTION, SAID CHECK VALVE OFFERING A SUBSTANTIALLY GREATER RESISTANCE TO FLOW FROM SAID MOTOR TOWARD SAID ACCUMULATOR THAN TO FLOW FROM SAID ACCUMULATOR TOWARD SAID MOTOR, SAID HYDRAULIC SYSTEM BEING SO CONSTRUCTED THAT SAID ACCUMULATOR AND OTHER SYSTEM COMPONENTS CAN SAFELY WITHSTAND THE MAXIMUM PRESSURES DEVELOPED IN SAID SYSTEM EVEN IN THE ABSENCE OF SAID CHECK VALVE. 